The high hydraulic conductivity of three wooded tropical peat swamps in northeast Peru: measurements and implications for hydrological function

Abstract

The form and functioning of peatlands depend strongly on their hydrological status, but there are few data available on the hydraulic properties of tropical peatlands. In particular, the saturated hydraulic conductivity (K) has not previously been measured in neotropical peatlands. Piezometer slug tests were used to measure K at two depths (50 and 90 cm) in three contrasting forested peatlands in the Peruvian Amazon: Quistococha, San Jorge and Buena Vista. Measured K at 50 cm depth varies between 0.00032 and 0.11 cm s À1 , and at 90 cm, it varies between 0.00027 and 0.057 cm s À1 . Measurements of K taken from different areas of Quistococha showed that spatial heterogeneity accounts for~20% of the within-site variance and that depth is a good predictor of K. However, K did not vary significantly with depth at Buena Vista and San Jorge. Statistical analysis showed that~18% of the variance in the K data can be explained by between-site differences. Simulations using a simple hydrological model suggest that the relatively high K values could lead to lowering of the water table by >10 cm within~48 m of the peatland edge for domed peatlands, if subjected to a drought lasting 30 days. However, under current climatic conditions, even with high K, peatlands would be unable to shed the large amount of water entering the system via rainfall through subsurface flow alone. We conclude that most of the water leaves these peatlands via overland flow and/or evapotranspiration.

Seasonal variability in methane and nitrous oxide fluxes from tropical peatlands in the western Amazon basin

“…Ebullition-driven CH 4 uptake is not a commonly reported phenomena in other peatland studies because it is likely an artefact of chamber sampling methods; as a consequence, we do not discuss these data further here. To summarize, these data on diffusive CH 4 flux and ebullition suggest that peatlands in the Pastaza-Marañón foreland basin are strong contributors to the regional atmospheric budget of CH 4 , given that the four vegetation types sampled here represent the dominant cover types in the PMFB (Draper et al, 2014;Householder et al, 2012;Kelly et al, 2014;Lahteenoja and Page, 2011) The overall trend in the diffusive flux data was towards greater temporal (i.e., seasonal) variability in diffusive CH 4 flux rather than strong spatial (i.e., inter-site) variability. For the pooled dataset, diffusive CH 4 emissions were significantly greater during the wet season than the dry season, with emissions falling by approximately half from one season to the other (i.e., 51.1 ± 7.0 to 27.3 ± 2.7 mg CH 4 -C m −2 day −1 ).…”

“…We established 239 sampling plots (∼ 30 m 2 per plot) within five tropical peatland sites that captured four of the dominant vegetation types in the region (Draper et al, 2014;Householder et al, 2012;Kelly et al, 2014;Lahteenoja and Page, 2011) and which encompassed a range of nutrient availabilities (Fig. 1, Table 1) (Lahteenoja and Page, 2011;Lahteenoja et al, 2009a).…”

“…Since the identification of extensive peat forming wetlands in the north (Lahteenoja et al, 2009a, b;Lahteenoja and Page 2011) and south (Householder et al, 2012) of the Peruvian Amazon, several studies have been undertaken to better characterize these habitats, investigating vegetation composition and habitat diversity (Draper et al, 2014;Kelly et al, 2014;Householder et al, 2012;Lahteenoja and Page, 2011), vegetation history (Lähteenoja and Roucoux, 2010), C stocks (Lahteenoja et al, 2012;Draper et al, 2014), hydrology (Kelly et al, 2014), and peat chemistry (Lahteenoja et al, 2009a, b). Most of the studies have focused on the PastazaMarañón foreland basin (PMFB), where one of the largest stretches of contiguous peatlands has been found (Lahteenoja et al 2009a;Lahteenoja and Page, 2011;Kelly et al, 2014), covering an estimated area of 35 600 ± 2133 km 2 (Draper et al, 2014).…”

“…Most of the studies have focused on the PastazaMarañón foreland basin (PMFB), where one of the largest stretches of contiguous peatlands has been found (Lahteenoja et al 2009a;Lahteenoja and Page, 2011;Kelly et al, 2014), covering an estimated area of 35 600 ± 2133 km 2 (Draper et al, 2014). Up to 90 % of the peatlands in the PMFB lie in flooded backwater river margins on floodplains and are influenced by large, annual fluctuations in water table caused by the Amazonian flood pulse (Householder et al, 2012;Lahteenoja et al, 2009a).…”

“…These nutrientpoor bogs are dominated by large, C-rich forests (termed "pole forests") that represent a very-high-density C store (total pool size of 1391 ± 710 Mg C ha −1 , which includes both above-and belowground stocks), exceeding even the C density of nearby floodplain systems (Draper et al, 2014). Even though the peats in these nutrient-poor bogs have a relatively high hydraulic conductivity, they act as natural stores of water because of high rainwater inputs (> 3000 mm per annum), which help to maintain high water tables, even during parts of the dry season (Kelly et al, 2014).…”